A conventional bicycle seat is connected to the top of the seat tube which is inserted into the seat tube of a bicycle frame. The height of the seat needs to be adjusted for different users. When riding along a downward road, the bicycle frame tilts an angle so that the rear portion of the bicycle frame is higher than the front portion so that the seat becomes higher and may hit the user's hip. Therefore, the seat needs to be lower to avoid possible injury.
The conventional bicycle seat adjustment device is located between the seat and the bicycle frame, and generally includes an inner tube and an outer tube in which the inner tube is received. A pneumatic cylinder or hydraulic cylinder is located between the inner and outer tubes. The position rod extends out from an end of the cylinder and compressed by a lever which is pivotably connected to a fixing member located at the underside of the seat. By operating the lever to push the piston rod, the piston rod is lowered or extended due to the changes of the paths in the cylinder. The movement of the piston rod moves the seat to a desired position.
A conventional bicycle seat adjustment device is disclosed in Taiwan Patent Application No. 089221346 and comprises a fixing member connected to the underside of the seat. A driving hole is defined through the fixing member and a lever is pivotably connected to the fixing member. The lever has an end that contacts the driving hole and the other end extends so it can be operated by the user. A guide rod has a polygonal cross section and is fixed to the underside of the fixing member. The guide rod includes a groove. The guide rod includes a passage and a pin slidably received in the groove. The pin has one end extending out from the driving hole of the fixing member and contacts one end of the lever. A spring is mounted to the pin and located between the lever and the fixing member. A soft pad is matches the shape of the groove and is engaged with the groove. A hollow tube is mounted to the guide rod and has two holes in the top end thereof. A threaded end piece is connected to the bottom end of the hollow tube. A pressure tube is located in the hollow tube and located beneath the guide rod. A piston is movably received in the pressure tube. The piston includes a front driving rod and a rear driving rod which is in contact with the front driving rod. The front and rear driving rods cooperate with multiple rings and control apertures to control the movement of the guide rod. A head piece is a hollow member and is mounted to the top end of the hollow tube. A reception room is defined in a side of the head piece and communicates with the central passage of the head piece. Two threaded holes are defined in two vertical walls of the reception room and a threaded rod extends through the two threaded holes. Two adjustment blocks are two curved blocks and the inner diameter of the two blocks are matched with the polygonal outer contour of the guide rod and the outer diameter of the blocks can be forced into the hollow tube. Each adjustment block has an engaging piece which is located corresponding to the passage of the hollow tube. When the two adjustment blocks are mounted to the guide rod, the engaging pieces are located in the holes of the hollow tube.
The guide rod is connected with the pressure tube, by the cooperation of the front and rear driving rods and the multiple rings, the guide rod is moved, so that the user can operates the lever to adjust the seat.
However, the pressure tube is received in the hollow tube and is not well positioned. When the guide rod and the piston move, the pressure tube may rotate and shift off from the center to affect the adjustment of the seat. Furthermore, when the guide rod and the piston move, the pressure tube is moved relative to the guide rod and the piston, so that the bottom end of the guide rod hits the top of the pressure tube, and this may lead to leakage and generate noise.
The present invention intends to provide a bicycle seat adjustment assembly to improve the shortcomings of the conventional seat adjustment device.